1. Field
The presently disclosed subject matter relates to a vehicle lamp including a vehicle headlamp attached to the front of a vehicle such as a car, and more particularly to a vehicle headlamp including a daytime running lamp in a headlight, an auxiliary headlight, spot light, traffic light, and the like.
2. Description of the Related Art
A conventional headlight is usually attached to the front of a vehicle such as a car with the purpose of illuminating the road ahead. The light can be used anytime, but particularly during periods of low visibility like at night or during precipitation. The conventional headlight includes a high beam for illuminating the road far ahead when other vehicles (e.g., oncoming cars) are not in front of the driven vehicle, and includes a low beam for illuminating the road near ahead so as not to generate a glare when vehicles like oncoming cars approach towards the driven vehicle. Therefore, the high beam is directed in a slightly upward-leftward direction and the low beam is directed in a slightly downward-rightward direction.
A conventional auxiliary headlight is used as a vehicle lamp that provides a light distribution similar to the above-described conventional headlight when attached to the front of a vehicle such as a car. The conventional auxiliary headlight includes a fog lamp, a spot lamp and a driving lamp. The fog lamp is used for illuminating the road ahead during periods of low visibility such as when fog is present, the spot lamp is used for providing a high beam light distribution during periods of high-speed driving, and the driving lamp is basically used for compensating for both low beam and fog lamps. Therefore, a light distribution of a fog lamp is broad and directed toward the road, the light distribution of a spot lamp is concentrated far ahead in a direction toward the road, and the light distribution of a driving lamp is somewhere in the middle between a fog lamp and a spot lamp.
The above-described headlight and auxiliary headlight collectively define a vehicle headlamp. The above-described conventional vehicle headlamp is configured with a structure, for instance, as shown by FIG. 9. A vehicle headlamp 1 is a parabolic typed headlight or auxiliary headlight, which includes a bulb 2, a reflector 3 and a driving circuit 4.
The bulb 2 is a conventional bulb that is used for a conventional vehicle headlamp, for example, a halogen bulb. The reflector 3 is configured with a parabolic reflex surface, which has a focus F located near a light-emitting portion of the bulb 2 and a symmetrical axis that extends horizontally toward the light-emitting direction of the vehicle headlamp 1. An inner reflex surface of the reflector 3 includes not only a revolved surface of a parabola but also a free surface that is based on a parabolic surface.
The driving circuit 4 is configured with well-known circuits to supply the bulb 2 with a driving voltage from a battery via a switching circuit and the like. Therefore, when the driving circuit 4 supplies the bulb 2 with the driving voltage, the bulb 2 of the vehicle headlamp 1 emits light and illuminates the road ahead.
According to the vehicle headlamp 1 made by the above-described configuration, one direct portion of the light emitted from the bulb 2 illuminates directly in the light-emitting direction of the vehicle headlamp 1 and another reflected portion of the light illuminates the road indirectly by being reflected from the reflector 3 in the light-emitting direction of the vehicle headlamp 1. The direct portion and reflected portion of light are formed as approximately horizontal parallel beams, respectively, and form a light distribution pattern, for example, for a fog lamp as shown by FIG. 10. In this case, a central maximum luminosity is approximately 5,250 cd when the driving voltage is 12.8 V.
Recently, a daytime lighting (or running lighting) used with respect to a vehicle headlamp such as a headlight and an auxiliary headlight has held public attention in order to improve visibility of a vehicle from the perspective of other vehicles and in view of safe driving considerations. However, daytime lighting of the conventional vehicle headlamp 1 shown in FIG. 9 may cause an overload of a battery. Therefore, recently, vehicles have been provided with an additional vehicle lamp used for a daytime running lamp, which is different from the vehicle headlamp 1 and is a small lamp having small power consumption. However, providing such a daytime running lamp results in a high cost for the vehicular lamps because of the addition of a new vehicle lamp in addition to the conventional vehicle headlamp 1.
Under the circumstances, a method for using a fog lamp of an auxiliary headlight as a daytime running lamp is well-known as shown in FIG. 11. The difference between FIG. 9 and FIG. 11 is an addition of a control circuit 5 located between the bulb 2 and the driving circuit 4 in the vehicle headlamp of FIG. 9. The method allows the light distribution for a daytime running lamp to not generate a glare in a central maximum luminosity by reducing the maximum luminosity, for example, to less than 1,000 cd. The driving voltage can be reduced by supplying, for example, 4V, from the driving circuit 4 via the control circuit 5. Thus, the method may result in forming a light distribution for a daytime running lamp as shown in FIG. 12.
The above-described control circuit 5 is configured with a resistor, PWM circuit and/or the like to reduce a voltage of a battery. Therefore, the control circuit 5 enables a low driving voltage to be supplied to the bulb 2 in order to form a light distribution for a daytime running lamp.
When the bulb 2 is a halogen bulb, a halogen cycle is generated in the bulb 2 during lighting. A halogen cycle is characterized as follows: tungsten evaporates from a filament of the light source; the tungsten combines with a halogen and circulates in the bulb 2; the tungsten near the filament separates from the halogen by heat of the filament; and the evaporated tungsten returns to the filament. The halogen cycle enables a halogen bulb to extend its life. However, a halogen cycle can be generated due to the combining of tungsten with a halogen when a halogen is more than 250 centigrade degrees in general.
As described above, the method for using a fog lamp as a daytime running lamp can involve the reduction of the driving voltage of bulb 2 to, for example, 4V. However, when the control circuit 5 supplies the bulb 2 with such a low voltage, a halogen cycle may not be generated because halogen in the bulb 2 cannot become more than 250 centigrade degrees. Thus, the tungsten adheres to an inner surface of glass of the bulb 2 and the life of the bulb 2 is extremely shortened. In addition, light-emitting luminosity of the bulb 2 decreases because of the tungsten adhered to the inner surface of the glass.
Furthermore, a light-emitting intensity distribution for the light distribution pattern for a daytime running lamp shown in FIG. 12 is basically the same as that for the fog lamp. A central maximum luminosity is higher than other portions, for example, 945 cd when a driving voltage is 4V. Thus, because the light distribution pattern is bright only in a central portion and is very dark around the central portion, visibility of the driven vehicle decreases.
On the other hand, a headlight that provides both a movable upper portion of a reflector and a movable shade is disclosed in patent document No. 1 (Japanese Utility Model Patent Application Laid Open H07-001503). The headlight can move both an upper portion of a reflector and a shade. In the case of high beam mode, the headlight has the shade moved so that the shade does not prevent emission of light rays from a light source and has the upper portion of the reflector moved so that a focus thereof is located near the light source. Thus, because the light source illuminates forwards in the light-emitting direction of the headlight by reflecting at least a portion of the light thereof via both the upper portion of the reflector and the under portion, the headlight can form a light distribution for a high beam.
In the case of low beam mode, the headlight has the shade located in the light path of the light source so that the shade prevents at least a portion if light from the light source from passing towards the upper portion of the reflector. At the same time, the upper portion of the reflector can be located so that the focus thereof is located at a position spaced far from the light source. Thus, because the light source illuminates the road in a forwards-downwards direction and in the light-emitting direction of the headlight by reflecting a light thereof via the under portion of the reflector, the headlight can form a light distribution for a high beam.
As described above, the movements of both the shade and the upper portion of the reflector enable the headlight to form both a high beam and a low beam light distribution pattern. However, patent document No. 1 does not disclose, among other features, the headlight being used as a daytime running lamp. Thus, patent document No. 1 is perfectly different from the disclosed subject matter in purpose, structure, effect and the like.    1. Patent document No. 1: Japanese Utility Model Patent Application Laid Open H07-001503
The disclosed subject matter has been devised to consider the above and other problems and characteristics. Thus, an embodiment of the disclosed subject matter can include a daytime running lamp with a simple structure and a favorable light distribution pattern in a parabolic typed headlight or auxiliary headlight, and the daytime running lamp can be driven by a driving voltage that can generate a halogen cycle in order for the halogen bulb to enjoy a long life.